1. Field of the Invention
The present invention relates to a scanner, more particularly, to a scanner with a groove in its scanning surface for reducing sticking effect caused by a document with viscous membrane.
2. Description of the Prior Art
Sheet-fed scanners are frequently used for scanning small documents into computers. Please refer to FIG. 1 and FIG. 2. FIG. 1 is a perspective view of a prior art sheet-fed scanner 10. FIG. 2 is a sectional view along line 2--2 of the scanner 10 shown in FIG. 1. The scanner 10 comprises an image pickup module 12, and a cylindrical document roller 14 rotatably mounted at one side of the image pickup module 12. The image pickup module 12 comprises a housing 11, a scanning surface 16 which is a transparent glass installed at one side of the housing 11 facing the roller 14, a light source 22 which is a light emitting diode (LED), and an elongated light sensor 24. Both the light source 22 and light sensor 24 are installed below the scanning surface 16 inside the housing 11. The scanning surface 16 has a line-shaped scanning position 18 parallel to the light sensor 24. When a document 26 is carried through the scanning position 18, the light 28 emitted from the light source 22 will be reflected from the document 26 over the scanning position 18 and received by the light sensor 24. The document roller 14 is driven by a stepping motor (not shown), and is rotatably mounted against the scanning surface 16 for carrying the document 26 through the scanning position 18 backward. When the document 26 is carried through the scanning surface 16 by the roller 14 at a constant speed, the image on the document 26 will be scanned by the light sensor 24.
When a photo picture which comprises viscous membrane on the picture surface is carried through the scanning surface 16, the roller 14 will press the viscous membrane against the scanning surface 16 which may be stuck to the scanning surface. Such sticking effect will interfere with the light reflected from the photo picture and generate a blurred image in the scanned image. Moreover, the sticking effect will greatly increase the viscosity between the photo picture and the scanning surface 16 which will drag the photo picture to prevent it from moving through. Sometimes the photo picture may completely get stuck on the scanning surface 16.